1. Field of the Invention
This invention relates to fluid pumping apparatuses, systems and methods, and more particularly to high-pressure pumps intended for use with common-rail fuel injection systems.
2. Description of the Related Art
Most fluid pumps have of necessity chambers and valves to move the fluid through the pump as it is pressurized and/or depressurized. The valves generally consist of a valve member and a biasing force imparted by means of a spring or spring assembly that continuously urges the valve member against a valve seat. To move the fluid through the valve, the valve is opened by moving the valve member away from the valve seat through the application of a momentary hydraulic, mechanical, electromagnetic or other force that overcomes the continuous biasing force. After fluid movement through the valve, the valve is closed by easing the momentary force and allowing the biasing force to close the valve member against the valve seat. A common example of this are solenoid valves, which use a spring to keep the valve member biased against the valve seat. The valve member is momentarily moved away from the valve seat through activation of the solenoid, which imparts an electromagnetic force that acts oppositely of and overcomes the spring's biasing force. Other valves use the pressure of the fluid itself to overcome the force of the spring, either through positive pressure (pressurization of the fluid) or negative pressure (depressurization of the fluid).
In some systems, particularly some fuel injectors and similar devices, the biasing force continuously urges the valve open, which is then momentarily closed by means of the oppositely directed hydraulic or electromagnetic force.
The particular area to which one embodiment of the invention pertains is common-rail fuel injection systems, widely used in diesel engines. These systems utilize high pressures with commensurate stresses on the system, and improved forms of the injection systems utilize higher pressures still. Among other things, these pressures cause problems with internal drilling intersections, which provide stress concentrations that reduce pressure and durability limits through stress fractures and the like. A particular instance of this would be a pump which contains an intake valve through which fuel is directed from an intake into a pressurizing chamber, and an outtake valve located adjacent the intake valve through which fuel is directed from the pressurizing chamber to an outtake discharge. The drilling intersections into the pressurizing chamber required to locate the intake and outtake valves in such a fashion create undesirable stress concentrations.
In many cases, the pump or pumps that supply fuel to the common rail must be capable of delivering fuel at a level of 1800 bar (about 26,000 psi) or higher. Various pump constructions and pumping methods are used to do this, each of them with their strengths and weaknesses. Many current pumps use 8-millimeter-diameter or 10-millimeter-diameter pumping or pressurizing plungers, with a 10- to 13-millimeter plunger stroke. The fuel moves from the common rail to the fuel injectors themselves for injection into the cylinders.
In pumping fuel from a fuel supply to a common rail, and in other systems where pumps are used, springs and similar mechanical devices that bias valves in their default positions complicate the system, providing additional mechanical moving parts that are subject to wear, maintenance, and replacement due to the high-pressure fuel moving through the system, rapid and repeated movement of the valves, and other stresses. As they experience wear, springs in this environment can generate debris that negatively affects the system. Springs experience fatigue, and wear on a spring can change its force characteristics. A spring's resonant frequency can also affect the system's operation.
From the foregoing discussion, it is apparent that a need exists for an improved apparatus, system, and method for pumping fluids.